Electric-current transmission



1,64 s1 oct. 25.1927. A' M CURTIS k 6 1 ELECTRIC CURRENT TRANSMISS ION Filed Dec. '7, 1925 Patented Det. 25, 1927.

narran stares israel raient orrica.

AUSTEN IVI. CURTIS, OF EAST ORANGE, NEW JERSEY, ASSIGNOR TO WESTERN LEC- TRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

ELECTRIC-CURRENT TRANSMSSION.

This invention relates to electric current transmission systems and to amplifiers and circuits for association therewith, and aims for simplicity and efliciency in transferring signals between an ampliiier and a circuit for connection to the amplifier input or output, especially where disturbance due to un desired currents, such for instance as currents resulting trom the tendency ot the amplifier to oscillate and 'from voltages in'- duced in the system by extraneous sources, should be guarded against; and more especially where direct current or other very low Yfrequency current is to be transmitted between the amplifier and the circuit or the use ot a transformer tor connecting the amplilier to the circuit is objectionable.

in accordance with the invention, substantially the whole of' th-e signal voltage across either the amplifier or the circuit may be tranimitted to the other without necessitating the employment ot a transformer,

and yet disturbances due to voltages im-` pressed on the line trom extraneous sources and to the tendency ot the amplifier to oscillate are prevented, without seriously impairing the transmission efliciency of the system Jfor the signals.

The amplifier may be directly connected to the circuit, tor instance a twin conducto-r cable balanced as regards the mpedances of its conductors to earth, without disturbing such balance, and without seriously reducing the efficiency oi the amplifier or ot the cable, and at the' same time the amplifier is effectively stabilized with relation to its surroundings tor the higher frequencies, at which oscillation might occur were the amplifier not so stabilized. The direct connection ot the amplifier to the cable avoids any necessity tor a connecting transformer which might be difficult to design and construct.

lt is also an object of the invention to reduce disturbance in a system in which signais are transferred through two circuits that are connected by an amplifier and ef;- posed to interference 'from extraneous electric fields.

rThe invention permits signalsl to be trans Jferred Yfrom one two-conductor balanced cable, by means ot an effectively earthed This application filed December space discharge amplifier, to a second balanced cable, without permitting either cable to be unbalanced by the amplifier or bv the other cable, and enables this to be donevwith only one transformer in the amplifier circuit. It also allows an effectively earthed amplifier to be directly connected to a twoconductor balanced cablewithout the use ot a transformer and without destroying the balance to earth of the two conductors of the cable.

In accordance with the invention an elec tric space discharge amplifier which con nects an incoming circuit that has its two sides balanced, with respect to their impedances between ground and the amplitier, to an outgoing circuit balanced as regards the impedances ot its two sides to ground, is stabilized, and at the same time interference eficcts due to the action ot extraneous electrical lields upon either circuit is minimized by preventing either circuit from being unbalanced by the amplifier or the other circuit, even though the impedance to ground ot each circuit be such as to be capable ot materially unbalancing the other circuit were that impedance connected to the two conductors of that other circuit asymmetriially with respect to those two conductors, f or instance as a result ot conductive connection of each circuitto the space discharge device of the amplier. i c u In the forms ot the invention specifically described hereinafter by reference to the ad companying drawing, a space discharge amplifier with a cathode, anode and control electrode has its cathode connected to one side ot' a circuit with which it is to be asociated and one ot the other electrodes connected to the other side of the circuit, and the end ot the circuit adjacent the amplifier is shunted by a circuit comprising two condensers in series, the junction point ot the condenser being grounded. rlhe amplifier 4is thus earthed locally through one oi the Y l Ce In one of the forms of the invention shown 1n the drawing, the amplifier having an 1nput set and an output set of electrodes is stablized and has one of the sets of elecamplifier end or shallow water section of the i sea cable may be exposed.

Other Vobjects and advantages of the invention will be apparent from the following detailed'description in connection with the accompanying drawing, wherein each of the figures illustrates an application of the in- Vvention in submarine cable telegraphy, al-

though it is not limited to such application. Fig. 1 is a circuitdiagram showinc' a way in which the invention can be applied to the connection of the output of an amplifier to a. circuit, and :also a way in which the invention can be applied tothe stabilization of an electric space discharge amplifier and the connection of the amplifier between two circuits in such manner as to prevent either circuit from being unbalanced by the stabilized amplifier or by the other circuit; and Fig. 2 is a circuit diagram showing away in which the-invention can be applied to the connec-V tion of a circuit tothe input of an amplifier. The cable systems herein described are `adapted/for use with submarine cables of such great length, as transoceanic Cables for example, that signals arriving from the cable are greatly attenuated, and, even after shaping and amplification, may be almost 'conipletely mashed rbyextraneous disturbances unless some means are provided for eltec-tively reducing the effect of disturbing magnetic fields upon the cable. Such means may. however, become of use in other types of signaling systems as the severity of operating conditions increases.

In the drawing, 1 is intended to represent a K cable. for example a loaded submarine cable having large distributed capacity, in-

.ductance and resistance, and 2 is intendedto represent a direct. ai'nplifying type of electric'space discharge amplifier for receiving4 telegraph signalsfrom the cable 1 and transmitting them through a circuit 10 to a receiving device 12, for instance a siphon recorder. The term direct amplifying type is used in the specification and claims to define an amplifier that increases the energy tion.

of an electric wave without shifting or converting'the frequency of the wave before, during, or after amplification.

The cable 1 comprises a single core section 3 terminated in a. twin core section fl. One core 5 of the twin core section ais connected at one end to the single core section 3 and at the other end to oneterminal of signal receiving apparatus which comprises shaping network 19, input transformer 20 and amplifier 2 and which will be presently described. `The other terminal of the receivving'apparatus is connected to one end of the second core 6 of the twin core section 1, the other end of core 6 being connected through a resistance 7 toa conductor in contact with the sea water, to furnish an earth connec- As shown, the resistance is connected to the cable armor wires 8 at point 9, a. conventional grounding symbol being employed in the drawing, to indicate that the armor wires are earthed. The core 6 together with the network 7 grounded at the point- 9 constitutes a cable balancing return circuit, for instance of the type disclosed in Osborne Patent 1,390,580, September 13,- 1921. Each of the cores-5 and 6, and also the core of the single-core cable section 3, may be of the nickel-iron alloy loaded' type described and "in balancedir'elation to the main cable with respect to the receiver, acts (as pointed out in the Osborne patent just mentioned) to greatly reduce the voltage appearing between tlie terminals of the main cable and the balancing sea earth as the result of eX- traneous electric fields acting upon the length of the twin core cable which lies in shallow water; and the sea earth is located at a depth beyond which the effect of electric waves ofsignaling frequencies employed in the cable is negligible. The length of the core 6 required to place the sea earth connected at an adequate depth may be considerable, as indicated by the dotted portion of the twin corel cable section 4l. ln the case of a cable between New York and the Azores,.for instance, it has been found advisable to use a sea earth core, about one hundred miles in length at the western end of the cable.V y f The circuit 10 may be, for example, a twin conductor or full metallic land cable having a length ofthe order of 15 or 2O miles,.and comprising conductors 13 and 14, and exposed to inductive interference from electric railroad and power lines (not shown) which it parallels. The dotted portions of lines 13 and 14 are intended to indicate the considerable extent of circuit 10. The circuit 10 is balanced with respect to earth; that is, the

neeaeii impedances to ground trom the two sides 13 and 14 ot circuit 10 are substantially equal and its conductors are also transposed in order to balance it with respect to magnetic lields.

The amplifier 2 is indicated as a tour stage amplifier comprising vacuum tubes 15, 16, 17 and 13 in tandem. [in input transtormer for the amplilier is indicated at 20. Block 19 between the cable and transformer 20, and blocks 22 to 24 between the 'various stages ot the amplilier, indicate any desired signal shaping networks or elements, for example those disclosed in my Patent 1,624,396, issued April 12, 1927. My Patents 1,586,970 and 1,536,972, both issued .lune 1, 1926, and Lritish Patent 153,357 lto W'estern Electric Company, Limited, also illustrate the application et shaping networrs in a circuit similar to that in which the networks are here shown.

The tube 18 comprises an anode 25, a cathode 26 and a control electrode 2i', and each ot the other tubes ot the amplitier has similar electrodes. A battery supplies cathode heating current for the tubes, and space current is supplied to tubes 15 and 16 from a battery 35, to tube 17 'l'roiu a battery 40, and to tube 18 from a battery 41 through a resistance 42 preferably of several thousand ohms, and a resistance 43. The resistance 43 lis tor straightening the grid potential plate current characteristic et the tube 18, to reduce distortion, and is preferably of the Order ot' several. hundred ohms, but

may be omitted it' desired. Conductor 13 is connected to a point on battery 41 at the saine potential as that et' the junction oi' conductor 14 with resistance 42 so that, battery 41 will normally not send direct current through circuit 10.

Amplier 2 may have a possible voltage amplilication at some frequencies ot the or der et 25,000 times, and therefore should be earthed locally, or through a short sea earth cable ot low impedance, to prevent oscillation troubles, since otherwise the amplifier may be unstable or tend to oscillate. However, it this earth connection were made by earthing the cathodes of the amplilier directly as is customary with vacuum tube amplifiers, the land cable 10 would be unbalanced, as one et' its conductors 14 would be earthed directly through Athe amplitier. As this cable is exposed to strong iields trom power lines and electric railways, this unbalance ot its conductors to earth would cause voltages to appear' at its terminals which might be ot sutlieient amplitude to seriously distort the telegraph signals.

To prevent undue disturbance caused by the tendency of the amplifier 2 to oscillate, and at the same time avoid unbalancing the circuit 10, the output oli the amplilier when connected to the circuit 10 is shunted by two condensers 50 and 51 connected in series, and

the junction et the two condensers is earthed locally, or through a sho-rt sea earth cable ot low impedance, as at 52, the capacity et the condenser-s being 'suliiciently small to avoid unduly shunting the circuit 10 with respect to the output ot the amplilier at the signaling frequencies to be transmitted, yet sullic-iently large so that the amplilier with `its cathodes earthed through condenser 51 However, the invention is not limited to the specific values mentioned in this description, as ay certain reasonable proportion must be maintained between the impedance oli the shunted eondensers and the impedance of the circuits across which they areshunted in or der to prevent the strength ot the transmitted signals trom being materially reduced.,

ln a system such as that described the natural capacities to ground of the batteries 30, 35, and 45 are small in comparison to the capacity 51, and do not necessitate proportioning the capacities and 51 relatively to each other to take account of that natural capacity, in maintaining the capacities to ground of the two sides oit circuit 10 equal.

In Fig. 1 the amplifier input is connected to the submarine cable and sea earth by the transformer 20, the secondary winding ot which is surrounded by an electrostatic shield 20 et' copper, which is electrically connected` to the terminal of the secondary winding that is connected toground through condenser 51.

It', in the system ot Fig. 1, the sea cable and its balancing return circuit were conneeted to the amplilier conductively, instead of through transformer 20, the impedance to earth et the conductor 14 ot the land cable, 'in parallel with condenser 51. would be connected to core 0 ot the sea cable through the common Vfilament lead ot the an'iplilier, while core 5 would be connected to the grid oi? the amplifier tube 15 through the shaping network 19. This would unbalance the twin core sca cable by shunting Al l) assegni 9. A low 'frequency telegraph system com.- prising a long submarine telegraph cable, a second telegraph circuit, balanced as regards the impedances oit its two conductors to earth and subject to interterence trom extraneous electrical fields, and means including an electric space discharge amplifying device composed ol' direct amplifying units only connecting said cable to said circuit and maintaining the balanced condition ot said circuit, said means transmitting low frequency telegraph signals between said cable and said circuit, the in'ipedance to earth of said cable being such that it would materially disturb the balanced condition or' said circuit were said circuit eonductively connected to said cable through said discharge device.

it). A signaling system comprising a sul marine cable, a cable balancing return path there'tor, an electric space discharge receiving amplifier associated with said cable and said return path and having an anode and a cathode, a receiving instrument, a circuit of substantial length having one o'I its two conductors connected to said'cathode and its other conductor associated with said anode, said circuit connecting said amplilier and said receiving instrument, similar impedanees connected in series relation across said circuit, said cathode being connected to earth through at least one ot said similar impedances and only in such manner that the two sides of said circuit are balanced with respect to said earth, and said circuit having inherent impedance to earth at least as small for frequencies ol the signaling :trequency range, as a value of the order of the value oft said similar impedances, and means ttor preventing said receiving instrument connecting circuit from adversely attecting said cable balancing path in its function of minimizing voltages induced by electrical fields extraneous to the cable.

ll. ln a signaling system, a submarine cable, a cable balancing return circuit, a receiving amplifier associated with said cable and return circuit, a receiving instrument, a metallic circuit ot substantial length connecting said amplifier and said receiving instrinnent9 and signal repeating means for preventing said receiving instrument connecting circuit ilrom adversely aileecting said cable balancing circuit in its function of minimizing voltages inducedby electrical fields extraneous to the cable.

l2. AA low 'frequency telegraph system comprising a long submarine cable conductor, a return path therefor balancing the impedance of said cable conductor, and including a conductor which is earthed at sea and parallels said cable conductor to reduce the voltages induced by interfering electrical fields to which the shallow water section of said cable conductor may be sub jected, a. low frequency telegraph circuit 1whose conductors are balanced both as regards their impedance to earth and their exposure to extraneous magnetic fields, and means comprising an electric space discharge amplifying device, connecting the cable con di A.tor and its return path conductor to said telegraph circuit and maintaining the impedance balance bet-Ween the `cable conductor and its return path, said means transmitting low frequency telegraph signals between said circuit and said conductors7 and the impedance, to earth, ot said circuit being such that it would materially disturb said impedance balance of said cable conductor and its return path were said circuit connected conductively to said cable conductor and said return path conductor through said discharge device.

1B. l submarine cable signaling system comprising a long submarine cable `conductor, an electric space. discharge receiving ainpliiier therefor having its cathode or cathedes earthed through an impedance sulftlciently small to prevent the amplitier from oscillating, a balancing return path 'for said conductor, simulating the impedance of said conductor and including a conductor which is earthed at sea and parallels said cable conductor to reduce the voltages induced by interfering electrical tields to which the section ot the cable lying in shallow Water may be sul'iiected, a receiving circuit fed troni said amplifier and balanced as regards the impedances of its two sides to earth, said circuit being exposed to interference from extraneous electric fields, the impedance. to earth, ot' said circuit being such that it would exert upon the impedance balance ot said cable conductor and its return path a disturbing eii'ect ot magnitude material in comparison to any due to said cathode earthing impedance, were said circuit connected conductively to said cable conductor or said return path through said amplifier, and the impedances to earth of said-cable conductor and said return path being such as would materially disturb said balanced condition ot said circuit were said circuit connected con ductively to said return path or said cable conductor through said amplilier, and means connecting said cable conductor and said return path to said amplifier and preventing the impedance balance between said cable conductor and its return conductor from be ing disturbed by either said circuit or said cathode earthing connection, and preventing said balanced condition oi said circuit from being disturbed by said cable conductor and said return path.

14C. A system according to claim 10, said similar impedances having such values as to shunt trom said circuit a small part only ot' the currents of signaling frequencies.

l5. A system according to claim ll), said similar impedances consisting principally or" capacitative reactance.

16. A system according to claim 10, said similar' impedances consisting principally of capacitative reactance vand having such values as to shunt kfrom said circuit a small vpart only of currents of frequencies from zero to several hundred cycles per second.r

17. In combination, an electric space dis'- charge ampliiier, means for transmitting low frequency telegraph signals thereto, said means comprising a cable and a cable balancing return circuit therefor, said cable balancing return circuit comprising means for diminishing the .effects of extraneous intertering electric Waves to vwhich the receiving end-of the cable may be subject-ed, said last means comprising a conductor adjacent to and paralleling the conductor of the cable and extending from the receiving end loit the cableto a sea earth so far removed from the receiving end of the cable that the rcrmainder oi the cable will be in water of such depth that the effect of said extraneous Waves will be negligible, and said amplilier having a cathode or cat-hotles, and a connection to earth from said cathode or cathodes, the impedance of the latter connection being so lon:I that it would be capable ol substantially lessening said reduction of interference eiects if said4 amplier were connected conductivelyAV to said cable and its balancing return Circuit, and said irst 1nentioned means comprising means preventing said cathode eartliing connection `from so disturbing the balance to earth of said cable and its balancing return circuit as tordisturbV prising two condensersin series bridged across the junction bets/een one set of ampliiier terminals and the two-conductor circircuit to which said terminals are connected, the junction oi' said condensers being connected to an earthv conductor of low impedance. Y

in Witness whereof, I hereunto subscribe my name this 1st day of December, A. D. 1925.

AUSTEN M. CURTIS. 

